If Congress passed a bill requiring that farm workers’ immigration status be verified, enforcing it might prove as challenging as enforcing the immigration laws themselves. These laws are difficult to enforce because they must overcome the substantial mutual benefit of work agreements between farmers and the illegal immigrants they hire. Market forces can be powerful.

Illegal immigrants don’t just fill jobs; they also buy stuff with the money they earn, spurring demand and creating jobs in other parts of the economy.

Due to that mutual benefit, I suspect lawmakers will pass the bill only if there remain loopholes that allow businesses and migrants to continue circumventing strict enforcement of immigration laws. This way, Republican lawmakers can symbolically pander to anti-immigrant sentiment — stoked by high unemployment — without causing too much damage to the various businesses that rely on illegal labor.

It’s probably true that American citizens are less willing to work so hard for so little pay. Citizens and those with valid work status would also be more likely to complain about hazardous and unhealthy work environments. Afraid of being caught and deported, illegal immigrants are wary of complaining or reporting substandard work environments to the Occupational Safety and Health Administration and its local counterparts. So if employers could hire only legal workers, they wouldn’t just have higher wages to pay, but perhaps also higher costs of fully complying with health and safety regulations.

If, contrary to my expectations, immigration laws were strictly enforced, then farmers would likely recoup some of their increased costs from higher fruit and vegetable prices, which are low-skill labor intensive. Consumers would see higher prices for fruits and vegetables and might buy less as a result. We might also expect more imports from Mexico and other nations with cheaper labor and weaker labor laws.

A few unemployed people with legal work status might find work. But the employment effect for citizens could be smaller than some might expect, because illegal immigrants don’t just fill jobs; they also buy stuff with the money they earn, spurring demand and creating jobs in other parts of the economy. While it’s hard to tell how large these various effects may be, it’s hard to see how cracking down on illegal-immigrant labor would be a net gain for the economy.